Multi-level parallel converters are now in wide use. By using the parallel interleaving connection technique, a multi-level parallel converter can reduce output ripple currents and increase an output switch frequency, and therefore can reduce output inductance, which in turn reduces a size and cost of an inductor.
For example, a five-level power converter with a two-phase coupled inductor is in use; when a common mode current flows through coils on two magnetic cylinders of the coupled inductor, because magnetic fluxes generated by the coils on the two magnetic cylinders are in opposite directions, a common mode magnetic flux in upper and lower magnetic yokes is zero and the magnetic fluxes in the two magnetic cylinders generate a very high common mode magnetic potential, so that a magnetic leakage occurs in the air, and the magnetic leakage caused by the common mode current cannot be ignored.
When a high common mode current flows through, a large magnetic flux leakage exists on the coupled inductor, and the magnetic flux leakage causes an eddy current loss in a winding and causes a stray loss in a metal part outside the winding. In addition, the magnetic flux leakage further affects normal running of a surrounding magnetic component such as a Hall effect sensor or a current transformer (current transformer, CT) . Therefore, it has become an immediate challenge to reduce the magnetic leakage of the coupled inductor.